Have a Dissy upper...gonna get a 20" Bushy gov barrel...will I need a new bolt to go with the new barrel because the bolt is now "shaped" to work with the old dissy barrel? In the gov manual it says to never use switch bolts between guns...

One more thing: There shouldn't be a problem using a Rock River bolt and bolt carrier assembly group with a Bushy barrel right? A bolt is a bolt is a bolt, right? Shouldn't be any differences in specs right?

Thanks!

Right is only in question between equals. And while the strong do what they can, the weak suffer what they must--Thucydides

In all likelyhood, your existing bolt will work just fine, but you really should have headspace checked between the bolt and new barrel to be sure. GIs have no way to check headspace in the field, which is why they aren't supposed to mix bolts (though it does happen).

While it isn't a good idea to switch bolts back and forth between uppers/barrels all the time, an occasional barrel change isn't gonna do too much to hurt the bolt's lifespan.

Bolts and barrels are factory headspaced -- for the M16 that is. This means you can drop 'em in and not worry about them other than checking with the M16 "gage, headspace, field." (These run anywhere from $10 to $30 still sealed in the USGI mylar-alumimum pouch.)

If you use this gage you can swap bolts at will but you'll tire of it after a while. I recommend a complete bolt carrier group for each barrel. And I'd use the Bushmaster (or Colt's) parts.

If you buy a new barrel, just make sure it is head spaced correctly just like Troy have stated. You will not need a new bolt, it will be fine the way it is. If you are buying a new upper and you are switching between uppers, then it is a good idea to get a different bolt and head space it according to your new upper. but since you are just getting a new barrel for your existing upper, you just need to make sure your head space is correct on the new barrel to the existing bolt.

Yes, a bolt is a bolt is a bolt, RRA and Bushmaster should be all the same as far as spec is concern. I use Bushmaster bolts exclusively, it has not failed me yet.

for safety, have the barrel installed by a gunsmith who has the guages and will finish chamber the barrel to your bolt after mounting the barrel on your upper. ANY manufacturer who says send in your bolt and they will headspace it for your barrel is BS'ing you..too many variants unless on YOUR upper receiver.

JusD --
The receiver has nothing do do with the headspace of a M16/AR15 barrel or bolt, that's why it's not BS that you don't need a gunsmith do to this, nor do you need any gage other than "gage, headspace, field." The permanent barrel extension controls the barrel part of headspace, the bolt controls it's own part.
New spec bolts and barrels will always headspace correctly. To ensure spec I stick with Bushmaster and Colt's barrels. There may be others but.....
-- Chuck

Chuck--
So all I need to check headspace is a set of those gages? I read the tacked post explaining the difference in military gages and civilian gages...confused the hell out of me though.
But are theses gages all that one needs to do the headspace thing?
thanks.

Right is only in question between equals. And while the strong do what they can, the weak suffer what they must--Thucydides

A new Bushmaster or Colt's barrel and new bolt will always be within the correct headspace tolerances, they're individually gaged at the factory. If you insist on gaging, all you need to do is check the combination with the military M16 "gage, headspace, field" to insure they're not excessive. They won't be, not new barrels from these two sources, but you should still check. these are, after all, built by humans. You can do this before even assembling the barrel into the receiver.
There's only the one (1) gage used in the Army when rebarrelling rifles: the field gage.
Commercial ".223" gages are almost all well undersized. Some commercial FIELD/REJECT gages are smaller than the spec for a M16 NO-GO gage, meaning the rifle will be in perfect M16 condition and yes show as a reject. Using the wrong gage tells you nothing.
Based on gaging dozens of Bushmaster and hundreds of Colt's barrels and bolts I'd not hesitate a second in putting either of these new bolt in combination with a new barrel and just shooting the puppy. They'll gage even if you don't check 'em.
I don't have this confidence on other barrels or bolts.
-- Chuck